Powder coating compositions are already known which are curable on crosslinking and which comprise an epoxy-containing resin and a compound or resin having a cyclic acid anhydride group and a free carboxyl group. These compositions have actually useful properties. However, when the powder composition is made into a coating composition of the organic solvent type, the resulting composition is low in storage stability and further has the drawback that it is difficult for the liquid composition to have a high solids content. Also known are coating compositions of the organic solvent type which comprise a resin containing both epoxy and hydroxyl, and a cyclic acid anhydride, such as succinic anhydride or methylhexahydrophthalic anhydride, for curing the resin by crosslinking, whereas the acid anhydride has the drawback of being susceptible to hydrolysis, for example, owing to the presence of water in the pigment, diluting solvent, air, etc. and therefore impairing the storage stability and curability of the composition.